This invention relates to an X-ray tube, in particular to a stationary anode X-ray tube.
The stationary anode X-ray tube generally comprises a cylindrical evacuated envelope, a cathode having a filament and hermetically fixed to one end of the envelope, an anode or anode target hermetically fixed to the other end of the envelope opposite to the cathode, and cooling means disposed on the fixed-end side of the anode target to cool such anode target with a cooling water. The anode target has an electron-impact surface inclined to a horizontal plane perpendicular to the central axis of the anode target. Electrons emitted from the filament of the cathode when heated collide with the electron-impact surface to emanate X-rays in all directions. Here the electron-impact surface is heated to a high temperature by the electron-impact heat. In order to take out X-rays to the outside for effective industrial use, an X-ray transmitting window is attached to the side wall of the envelope adjacent to the anode target.
The X-ray transmitting window has conventionally been made of metal with small atomic number such as beryllium. However, it has been required to reduce the attenuation coefficient of X-rays. The X-ray transmitting window is generally liable to be heated to a high temperature by the radiant and conductive heat from the heated electron-impact surface as well as by collision of scattered electrons such as secondary electrons emitted from the electron-impact surface and stray electrons from the filament; the rise in temperature of the X-ray transmitting window is especially serious since such window is thin. The secondary electrons from the electron-impact surface, among other factors to heat the X-ray transmitting window, contributes much to heating of the X-ray transmitting window. In the conventional stationary anode X-ray tube, it has been very difficult to reduce the thickness of the X-ray transmitting window because such window is located right opposite to the inclined electron-impact surface, so that it is highly liable to be heated under the substantial influence of the secondary electrons.